1. Field of the Invention
The present invention relates to a channel estimation apparatus and method for Wideband Code Division Multiple Access (WCDMA) mobile communication terminals; and, more particularly, to an apparatus and method for channel estimation using a combination of Pilot Aided Decision Directed (PADD) algorithms and a non-linear filter.
2. Description of Related Art
In general, a forward system of Wideband CDMA has a channel structure in which data signals and pilot signals are time-multiplexed in communication channels of timeslot unit in order to increase its capacity. Accordingly, two of best-known channel estimation methods for a communication system with time-multiplexed data signals and pilot signals are Pilot-Aided (PA) algorithms and Decision-Directed (DD) algorithms.
FIG. 1 is a view of a diagram illustrating a channel estimation apparatus based on conventional PA algorithms.
There are several typical PA algorithms such as a Wiener Filtering, a Low-order Gaussian Interpolation, a Weighted Multi-Slot Averaging (WMSA), a High-order Interpolation and Linear Interpolation algorithms.
The PA algorithms in low-speed fading environments give a relatively high performance. However, the performance of the PA algorithms is decreased in high-speed fading environments. It is because a pilot signal of next slot is required for channel estimation so there is one time slot delay occurred for waiting for arriving next slot.
On the other hand, the DD algorithms outperform the PA algorithms due to the fact that the channel information carried by data signals is used in the calculation of the channel estimate. Nonetheless, the performance of the DD algorithms degrades in a case that decision errors are propagated.
To overcome the above-mentioned shortcomings, a Pilot-Aided Decision Directed PADD algorithm has been introduced. The PADD algorithm is a combination of PA algorithms and DD algorithms.
FIG. 2 is a view of a diagram illustrating a channel estimation apparatus based on conventional PADD algorithms.
In the PADD algorithm, preliminary channel estimation and data are decided at first by using a Linear Interpolation algorithm. After that, final channel estimation and data are obtained based on the channel information of data signals.
In the PADD algorithms, since channel estimations are performed by using data signals and pilot signals, the performance degradation and the propagation of decision error can be prevented. Therefore, the PADD algorithms perform better than Linear Interpolation algorithms and DD algorithms.
However, the PADD algorithms still has a time-delaying problem as PA algorithms and the implementation of the algorithms is more complex.